Wind power generation, wherein wind energy is converted into electricity, is constantly increasing as a power source. Representing a highly environmentally friendly alternative to other energy sources, wind power plants (WPPs), wherein wind turbine generators (WTGs) are agglomerated, are currently being developed and erected in numerous countries, both off-shore, onshore, and in the inland.
Although requirements for the connection of WPPs to the electrical grid may vary, common aims include permitting the development, maintenance and operation of a coordinated, reliable and economical transmission of electricity. However, as wind may frequently change both its direction and magnitude, the generated voltage from WTGs may be erratic. As an example, different wind speeds are translated into different active power generation levels, thus having different voltage levels for different wind speeds.
To compensate for an undesired fluctuation in the voltage supply and to counteract disturbances in the energy generation such as voltage sags, swells and momentary interruptions, reactive power equipment may be installed in the WPP. This equipment may for example include static compensators if the dynamic properties of the WPP are to be improved, switchable capacitors if the requirement is related to steady-state performance, or the equipment may comprise a combination of both static and switchable compensators.
The voltage from the WTGs and the reactive power equipment which is to be supplied to the grid is often transformed by a WPP transformer (WPPT). However, to counteract voltage disturbances in the power supply, there is a wish to improve the control of the WPPT such that grid requirements are fulfilled regarding the supplied electricity. However, such a control may be difficult to achieve, notably due to the number of WTGs being large and/or the reactive power equipment impact on the WPP.
Furthermore, if the voltage on the primary side of the WPPT is unstable—and possibly the voltage at the WTG terminals is too—the performance of an independent control of the voltage to be supplied to the electricity grid may deteriorate.